Information or content may be stored on a wide variety of media. As the speed and convenience of accessing and copying stored information have increased, the threat of unauthorized copying of the information has increased correspondingly. Various schemes have been employed to protect content stored on read-only media from unauthorized access by storing various types of data in different regions of the medium.
One such scheme can be illustrated in a medium such as a DVD-ROM (Digital Versatile Disc-Read Only Media), as illustrated in FIG. 1A. The medium 100 comprises a Data Area 102 and a Lead-In Area 104 (hereinafter referred to as a Non-Data Area 104). As further illustrated in FIG. 1B, the Data Area 102 comprises encrypted content 112 (or scrambled content in the case of DVD-Video content protected by the Content Scramble System (CSS)).
On a DVD-ROM disc that contains DVD-Audio content protected by CPPM, for example, the Control Data Area 110 (CDA 110) stores Keying Material 114 called an Album Identifier (and/or possibly Secure Disk Key Data in the case of DVD-Video content protected by the Content Scramble System). The Album Identifier is an 8-byte (64-bit) value that is randomly and individually assigned to each album to be protected. The cryptographic key needed to decrypt Encrypted Content 112 that is stored on the Data Area 102 of the medium is dependent on the Album Identifier value. Thus, if the Album Identifier is incorrectly copied to recordable media, for example, the incorrect Album I.D. will cause a player to form an incorrect cryptographic key, thus preventing the recordable medium from being played in a compliant manner.
For such content protection to be effective, it is ideal that recordable media be designed to prevent the sector that contains the Keying Material 114 (e.g., Album Identifier that is stored in Control Data Area 110, Sector #2 or CDA 110 Sector #2 in the case of a DVD-ROM) from being written such that the Keying Material 114 cannot be copied. However, some forms of recordable media, such as DVD-R (Digital Video Disc-Recordable) and DVD-RW (Digital Video Disc-ReWriteable), which have sectors/layout similar to the DVD-ROM layout depicted in FIGS. 1A and 1B, may contain writeable sector addresses which allow one to record Keying Material 114 in the Data Area 102 and assign it the address of the sector containing the Keying Material 114, such that a player may not be able to distinguish it from legitimate Keying Material 114. Of course, it is also possible that other media (such as non-compliant DVDRs and DVD-RWs) may allow the sector that contains the Keying Material 114 to be directly written.